Grid-forming control method for offshore wind turbine

Abstract

Disclosed is grid-forming control method for an offshore wind turbine, including the following steps: obtaining a grid voltage and current at a grid connection point of a wind turbine, actual values of active power and reactive power of the wind turbine, and references of the active power, the reactive power and an voltage amplitude; calculating a phase reference of a grid-side converter of the wind turbine; calculating a reference of a modulating voltage at the grid-side converter of the wind turbine in a dq rotating coordinate system; and calculating a reference of a modulating voltage at the grid-side converter in an abc static coordinate system according to the phase reference of the grid-side converter of the wind turbine and the reference of the modulating voltage in the dq rotating coordinate system. The present disclosure can control the voltage amplitude of the grid connection point by the active power of the wind turbine, and can control the voltage frequency at the grid connection point by the reactive power of the wind turbine. Furthermore, the wind turbine controlled by the present disclosure can be kept in reliable synchronous running under conditions of startup, power fluctuation, alternating current (AC) fault and the like.

Claims

1. A grid-forming control method for an offshore wind turbine, performed by a grid-forming system, wherein the grid-forming system is part of or in communication with the offshore wind turbine, and wherein the grid-forming control method comprises the following steps: S1, obtaining a grid voltage and a current at a grid connection point of the offshore wind turbine, performing a dq decomposition on the grid voltage and the current at the grid connection point of the offshore wind turbine to separately obtain d-axis components and q-axis components of the grid voltage and the current at the grid connection point in a dq rotating coordinate system, obtaining actual values of active power, reactive power, and voltage frequency at the grid connection point of the offshore wind turbine, and obtaining references of the active power, the reactive power and the voltage amplitude at the grid connection point of the offshore wind turbine; S2, calculating a phase reference of a grid-side converter of the offshore wind turbine; S3, calculating a d-axis voltage reference-of the grid connection point of the offshore wind turbine; S4, calculating a d-axis current reference and a q-axis current reference of the grid connection point of the offshore wind turbine; S5, calculating a d-axis voltage reference and a q-axis voltage reference of a modulating voltage of the grid-side converter of the offshore wind turbine; S6, calculating an a-axis voltage reference, a b-axis voltage reference, and a c-axis reference of the modulating voltage in an abc static coordinate system of the grid-side converter of the offshore wind turbine; and S7, generating, according to the references of the modulating voltages, a corresponding control pulse for each Insulated Gate Bipolar Transistor of the grid-side converter by pulse width modulation, to control the grid-side converter of the offshore wind turbine, thereby establishing a stable alternating current voltage for the offshore wind turbine and controlling the offshore wind turbine to keep synchronous running under conditions of startup, power fluctuations, or alternating current fault.

2. The grid-forming control method for the offshore wind turbine according to claim 1, wherein in the step S2, a calculation formula for the phase reference, *, of the grid-side converter of the offshore wind turbine is as follows: $^{*} = \frac{_{b a s e}}{s} [+ \frac{K_{G}}{1 + s K_{T}} (Q - Q_{r e f})]$ where s is a Laplace operator; .sub.base is a basic frequency of an AC system; is the actual value of the voltage frequency at the grid connection point; K.sub.G and K.sub.T are a proportion parameter and time parameter of a first-order inertial controller, respectively; Q is the actual value of the reactive power of the offshore wind turbine; and Q.sub.ref is the reference of the reactive power of the offshore wind turbine.

3. The grid-forming control method for the offshore wind turbine according to claim 1, wherein in the step S3, a calculation formula for the d-axis voltage reference, U.sub.d*, of the grid connection point of the offshore wind turbine is as follows: $U_{d}^{*} = U_{d 0} + (K_{P} + \frac{K_{I}}{s}) (P_{r e f} - P)$ where U.sub.d0 is the reference of the voltage amplitude at the grid connection point of the offshore wind turbine; K.sub.P and K.sub.I are a proportion parameter and an integral parameter of an active power PI controller, respectively; s is a Laplace operator; and P.sub.ref and P are the reference and the actual value of the active power of the offshore wind turbine, respectively.

4. The grid-forming control method for the offshore wind turbine according to claim 1, wherein in the step S4, calculation formulas for the d-axis current reference, I.sub.d*, and the q-axis current reference, I.sub.q*, of the grid connection point of the offshore wind turbine are as follows: ${\begin{matrix} I_{d}^{*} = - C_{F} U_{q} + (K_{P V} + \frac{K_{IV}}{s}) (U_{d} - U_{d}^{*}) \\ I_{q}^{*} = C_{F} U_{d} + (K_{P V} + \frac{K_{IV}}{s}) U_{q} \end{matrix}$ where U.sub.d and U.sub.q are a d-axis component and a q-axis component of the voltage at the grid connection point of the offshore wind turbine in the dq rotating coordinate system, respectively; s is a Laplace operator; is the actual value of the voltage frequency at the grid connection point; U.sub.d* is the d-axis voltage reference of the grid connection point of the offshore wind turbine; C.sub.F is a capacitance value of an AC side LC filter of the grid-side converter of the offshore wind turbine; and K.sub.PV and K.sub.IV are a proportion parameter and an integral parameter of a voltage controller, respectively.

5. The grid-forming control method for the offshore wind turbine according to claim 1, wherein in the step S5, calculation formulas for the d-axis voltage reference, V.sub.d*, and the q-axis voltage reference, V.sub.q*, of the modulating voltage of the grid-side converter of the offshore wind turbine are as follows: ${\begin{matrix} V_{d}^{*} = U_{d} - L_{F} I_{q} + (K_{P C} + \frac{K_{IC}}{s}) (I_{d}^{*} - I_{d}) \\ V_{q}^{*} = U_{q} + L_{F} I_{d} + (K_{P C} + \frac{K_{IC}}{s}) (I_{q}^{*} - I_{q}) \end{matrix}$ where I.sub.d and I.sub.q are a d-axis component and a q-axis component of the current at the grid connection point of the offshore wind turbine in the dq rotating coordinate system, respectively; L.sub.F is an inductance value of the AC side LC filter of the grid-side converter of the offshore wind turbine; K.sub.PC and K.sub.IC are a proportion parameter and integral parameter of a current controller, respectively; s is a Laplace operator; is the actual value of the voltage frequency at the grid connection point; and I.sub.d* and I.sub.q* are the d-axis current reference and the q-axis current reference of the grid connection point of the offshore wind turbine, respectively.

6. The grid-forming control method for the offshore wind turbine according to claim 1, wherein in the step S6, calculation formulas for the a-axis voltage reference, V.sub.a*, the b-axis voltage reference, V.sub.b*, and the c-axis voltage reference, V.sub.c*, of the modulating voltage of the grid-side converter of the offshore wind turbine in the abc static coordinating system are as follows: ${\begin{matrix} V_{a}^{*} = V_{d}^{*} \cos^{*} - V_{q}^{*} \sin^{*} \\ V_{b}^{*} = V_{d}^{*} \cos (^{*} - \frac{2}{3}) - V_{q}^{*} \sin (^{*} - \frac{2}{3}) \\ V_{c}^{*} = V_{d}^{*} \cos (^{*} + \frac{2}{3}) - V_{q}^{*} \sin (^{*} + \frac{2}{3}) \end{matrix}$ where * is the phase reference of the grid-side converter of the offshore wind turbine; and V.sub.d* and V.sub.q* are the d-axis voltage reference and the q-axis voltage reference of the modulating voltage of the grid-side converter of the offshore wind turbine, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Drawings described herein are used for providing further understandings of the present disclosure, and constitute one part of this application. Illustrative embodiments and descriptions thereof of the present disclosure are used for explaining the present disclosure, and do not constitute an improper limitation to the present disclosure. In the drawings:

(2) FIG. 1 is a flowchart of a grid-forming control method for an offshore wind turbine disclosed in the present disclosure; and

(3) FIG. 2 is a schematic diagram of a simulation waveform of a power fluctuation in a case of using the grid-forming control method of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) In order to make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below in combination with the drawings in the embodiments of the present disclosure. Obviously, the embodiments described herein are part of the embodiments of the present disclosure, not all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative work shall fall within the protection scope of the present disclosure.

Embodiment 1

(5) Referring to FIG. 1, this embodiment discloses a grid-forming control method for an offshore wind turbine, including the following steps:

(6) At S1, a grid voltage and current at a grid connection point of a wind turbine are obtained; dq decomposition is performed on the grid voltage and current at the grid connection point of the wind turbine to separately obtain d-axis components and q-axis components of the grid voltage and current at the grid connection point in a dq rotating coordinate system; actual values of active power, reactive power and voltage frequency at the grid connection point of the wind turbine are obtained; and references of the active power, the reactive power and the voltage amplitude at the grid connection point of the wind turbine are obtained.

(7) At S2, a phase reference of a grid-side converter of the wind turbine is calculated.

(8) A calculation formula for the phase reference * of the grid-side converter of the wind turbine is as follows:

(9) $^{*} = \frac{_{b a s e}}{s} [+ \frac{K_{G}}{1 + s K_{T}} (Q - Q_{r e f})]$

(10) where s is a Laplace operator; .sub.base is a basic frequency of an AC system; is the actual value of the voltage frequency at the grid connection point; K.sub.G and K.sub.T are a proportion parameter and time parameter of a first-order inertial controller, respectively; Q is the actual value of the reactive power of the wind turbine; and Q.sub.ref is the reference of the reactive power of the wind turbine.

(11) At S3, a d-axis voltage reference of the grid connection point of the wind turbine is calculated.

(12) A calculation formula for the d-axis voltage reference U.sub.d* of the grid connection point of the wind turbine is as follows:

(13) $U_{d}^{*} = U_{d 0} + (K_{P} + \frac{K_{I}}{s}) (P_{r e f} - P)$

(14) where U.sub.d0 is the reference of the voltage amplitude at the grid connection point of the wind turbine; K.sub.P and K.sub.I are a proportion parameter and integral parameter of an active power PI controller respectively; s is a Laplace operator; and P.sub.ref and P are the reference and actual value of the active power of the wind turbine, respectively.

(15) At S4, a d-axis current reference and a q-axis current reference of the grid connection point of the wind turbine are calculated.

(16) Calculation formulas for the d-axis current reference I.sub.d* and the q-axis current reference I.sub.q* of the grid connection point of the wind turbine are as follows:

(17) ${\begin{matrix} I_{d}^{*} = - C_{F} U_{q} + (K_{P V} + \frac{K_{IV}}{s}) (U_{d} - U_{d}^{*}) \\ I_{q}^{*} = C_{F} U_{d} + (K_{P V} + \frac{K_{IV}}{s}) U_{q} \end{matrix}$

(18) where U.sub.d and U.sub.q are a d-axis component and q-axis component of the voltage at the grid connection point of the wind turbine in the dq rotating coordinate system, respectively; s is a Laplace operator; is the actual value of the voltage frequency at the grid connection point; U.sub.d* is the d-axis voltage reference of the grid connection point of the wind turbine; C.sub.F is a capacitance value of AC side LC filter of the grid-side converter of the wind turbine; and K.sub.PV and K.sub.IV are a proportion parameter and integral parameter of a voltage controller, respectively.

(19) At S5, a d-axis voltage reference and q-axis voltage reference of a modulating voltage of the grid-side converter of the wind turbine are calculated.

(20) Calculation formulas for the d-axis voltage reference V.sub.d* and the q-axis voltage reference V.sub.q* of the modulating voltage of the grid-side converter of the wind turbine are as follows:

(21) ${\begin{matrix} V_{d}^{*} = U_{d} - L_{F} I_{q} + (K_{P C} + \frac{K_{IC}}{s}) (I_{d}^{*} - I_{d}) \\ V_{q}^{*} = U_{q} + L_{F} I_{d} + (K_{P C} + \frac{K_{IC}}{s}) (I_{q}^{*} - I_{q}) \end{matrix}$

(22) where I.sub.d and I.sub.q are a d-axis component and q-axis component of the current at the grid connection point of the wind turbine in the dq rotating coordinate system, respectively; L.sub.F is an inductance value of the AC side LC filter of the grid-side converter of the wind turbine; K.sub.PC and K.sub.IC are a proportion parameter and integral parameter of a current controller, respectively; s is a Laplace operator; is the actual value of the voltage frequency at the grid connection point; and I.sub.d* and I.sub.q* are the d-axis current reference and the q-axis current reference of the grid connection point of the wind turbine, respectively.

(23) At S6, an a-axis voltage reference, a b-axis voltage reference and a c-axis reference of the modulating voltage in an abc static coordinate system of the grid-side converter of the wind turbine are calculated.

(24) At S7, a corresponding control pulse is generated generating according to the references of the modulating voltages by using a pulse width modulation theory, to control the grid-side converter of the offshore wind turbine.

(25) Calculation formulas for the a-axis voltage reference V.sub.a*, the b-axis voltage reference V.sub.b* and the c-axis voltage reference V.sub.c* of the modulating voltage of the grid-side converter of the wind turbine in the abc static coordinating system are as follows:

(26) 0 ${\begin{matrix} V_{a}^{*} = V_{d}^{*} \cos^{*} - V_{q}^{*} \sin^{*} \\ V_{b}^{*} = V_{d}^{*} \cos (^{*} - \frac{2}{3}) - V_{q}^{*} \sin (^{*} - \frac{2}{3}) \\ V_{c}^{*} = V_{d}^{*} \cos (^{*} + \frac{2}{3}) - V_{q}^{*} \sin (^{*} + \frac{2}{3}) \end{matrix}$

(27) where * is the phase reference of the grid-side converter of the wind turbine; and V.sub.d* and V.sub.q* are the d-axis voltage reference and the q-axis voltage reference of the modulating voltage of the grid-side converter of the wind turbine, respectively.

Embodiment 2

(28) Based on the grid-forming control method for an offshore wind turbine disclosed in Embodiment 1, this embodiment performs simulation verification using a test system including four offshore wind turbines. All the wind turbines adopt grid-forming control referred to in the present disclosure. It is assumed that the active powers generated by wind turbines 1, 2, 3, and 4 in steady states are 300 MW, 150 MW, 100 MW, and 50 MW, respectively. System characteristics with linear and step changes in the active powers of the wind turbines are as shown in FIG. 2. At time t=4.0 s, the power of wind turbine 1 linearly decreases from 300 MW to 100 MW, with a change rate of 150 MW/s. At time t=6.0 s, the power of wind turbine 3 linearly decreases from 100 MW to 250 MW, with a change rate of 150 MW/s. At time t=8.0 s, the power of wind turbine 4 steps up from 50 MW to 300 MW. At time t=9.0 s, the power of wind turbine 2 steps down from 150 MW to 50 MW. As can be seen from the simulation FIG. 2, when the wind turbine has linear and step changes in the active power, the system can well track the change of the reference of the active power and reach a stable running state in very short time.

(29) The above embodiments are preferred implementations of the present disclosure, but the implementations of the present disclosure are not limited by the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications that are made without departing from the spirit essence and principle of the present disclosure shall all be equivalent replacement methods, which all fall within the protection scope of the present disclosure.

Grid-forming control method for offshore wind turbine

Assignee

Inventors

Cpc classification

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H02J3/0014

ELECTRICITY

Classification Explorer

H02J2101/28

ELECTRICITY

Classification Explorer

H02J3/36

ELECTRICITY

International classification

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H02J3/0014

ELECTRICITY

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H02J3/36

ELECTRICITY

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H02J3/38

ELECTRICITY

Abstract

Claims

Description